U.S. Pat. No. 4,367,342 discloses an olefin epoxidation process wherein an olefin is contacted with an organic hydroperoxide in the presence of an insoluble catalyst comprised of an inorganic oxygen compound of titanium. The patent discloses that at the conclusion of the reaction, the resulting product mixture may be separated and the products recovered by conventional methods such as fractional distillation, selective extraction, filtration and the like. The patent further teaches that the catalyst may be recycled for further utilization. Unfortunately, heterogeneous catalysts of the type disclosed in U.S. Pat. No. 4,367,342, for reasons which are not fully understood, tend to slowly deteriorate in performance when used repeatedly or in a continuous process for a prolonged period of time. In particular, the activity of the catalyst (as measured by the amount of olefin or organic hydroperoxide converted per pass or in a given period of time) decreases with time to a point where continued use of the catalyst charge no longer becomes economically viable. Due to the relatively high cost of synthesizing this type of catalyst, regeneration of the used catalyst would be greatly preferred over replacement.
It has previously been proposed that satisfactory regeneration might be achieved by blowing with hot air to burn away the impurities on the catalyst. However, heating the used catalyst at temperatures typically utilized for regeneration of other heterogeneous catalysts (e.g., zeolites), even for prolonged periods of time, fails to sufficiently improve the activity of the titanium-containing catalysts described hereinabove. Moreover, catalytic activity is not completely restored by heating at 500.degree. C., even though substantially all organic impurities in the catalyst are removed at such temperatures. Although we have found that significantly higher temperatures are effective for reactivation purposes, a regeneration process which operates at such elevated temperatures is not ideal due to the increased utility and construction costs associated therewith. Thus, it would be desirable to develop alternative regeneration methods capable of operating at lower temperatures such that regeneration could be easily performed in situ, i.e., the same vessel in which the epoxidation is carried out.